Pre-curved cochlear implant electrode array

ABSTRACT

An implantable electrode array ( 30 ) that can adopt a first configuration selected to allow the array ( 30 ) to be inserted into a cochlea ( 12 ) of an implantee and at least a second configuration in which the array can apply tissue stimulation. The array ( 30 ) comprises an elongate carrier ( 31 ) having a proximal end ( 37 ), a distal end ( 34 ), and an inner surface ( 35 ) conformable with the inner wall of the implantee&#39;s cochlea ( 12 ). A plurality of electrodes ( 36 ) are supported within the carrier ( 31 ) at respective spaced locations thereon in a region between the proximal end ( 37 ) and the distal end ( 34 ) with at least one of the electrodes having a surface that is at least adjacent the inner surface ( 35 ) of the carrier ( 31 ). The carrier ( 31 ) is formed in the second configuration from a first layer ( 32 ) and at least a second layer ( 32 ) of resiliently flexible material. A method of forming an array ( 30 ) is also described.

FIELD OF THE INVENTION

[0001] The present invention relates to an implantable device and, inparticular, to an implantable cochlear electrode assembly. A method ofmanufacturing such a device is also described.

BACKGROUND OF THE INVENTION

[0002] Hearing loss, which may be due to many different causes, isgenerally of two types, conductive and sensorineural. Of these types,conductive hearing loss occurs where the normal mechanical pathways forsound to reach the hair cells in the cochlea are impeded, for example,by damage to the ossicles. Conductive hearing loss may often be helpedby use of conventional hearing aid systems, which amplify sound so thatacoustic information does reach the cochlea and the hair cells.

[0003] In many people who are profoundly deaf, however, the reason fordeafness is sensorineural hearing loss. This type of hearing loss is dueto the absence of, or destruction of, the hair cells in the cochleawhich transduce acoustic signals into nerve impulses. These people arethus unable to derive suitable benefit from conventional hearing aidsystems, because there is damage to or absence of the mechanism fornerve impulses to be generated from sound in the normal manner.

[0004] It is for this purpose that cochlear implant systems have beendeveloped. Such systems bypass the hair cells in the cochlea anddirectly deliver electrical stimulation to the auditory nerve fibres,thereby allowing the brain to perceive a hearing sensation resemblingthe natural hearing sensation normally delivered to the auditory nerve.U.S. Pat. No. 4,532,930, the contents of which are incorporated hereinby reference, provides a description of one type of traditional cochlearimplant system.

[0005] Cochlear implant systems have typically consisted of two keycomponents, namely an external component commonly referred to as aprocessor unit, and an implanted internal component commonly referred toas a stimulator/receiver unit. Traditionally, both of these componentshave cooperated together to provide the sound sensation to an implantee.

[0006] The external component has traditionally consisted of amicrophone for detecting sounds, such as speech and environmentalsounds, a speech processor that converts the detected sounds andparticularly speech into a coded signal, a power source such as abattery, and an external antenna transmitter coil.

[0007] The coded signal output by the speech processor is transmittedtranscutaneously to the implanted stimulator/receiver unit situatedwithin a recess of the temporal bone of the implantee. Thistranscutaneous transmission occurs through use of an inductive couplingprovided between the external antenna transmitter coil which ispositioned to communicate with an implanted antenna receiver coilprovided with the stimulator/receiver unit. This communication servestwo essential purposes, firstly to transcutaneously transmit the codedsound signal and secondly to provide power to the implantedstimulator/receiver unit. Conventionally, this link has been in the formof a radio frequency (RF) link, but other such links have been proposedand implemented with varying degrees of success.

[0008] The implanted stimulator/receiver unit typically included theantenna receiver coil that receives the coded signal and power from theexternal processor component, and a stimulator that processes the codedsignal and outputs a stimulation signal to an intracochlea electrodeassembly which applies the electrical stimulation directly to theauditory nerve producing a hearing sensation corresponding to theoriginal detected sound.

[0009] The external componentry of the cochlear implant has beentraditionally carried on the body of the implantee, such as in a pocketof the implantee's clothing, a belt pouch or in a harness, while themicrophone has been mounted on a clip mounted behind the ear or on aclothing lapel of the implantee.

[0010] More recently, due in the main to improvements in technology, thephysical dimensions of the speech processor have been able to be reducedallowing for the external componentry to be housed in a small unitcapable of being worn behind the ear of the implantee. This unit hasallowed the microphone, power unit and the speech processor to be housedin a single unit capable of being discretely worn behind the ear, withthe external transmitter coil still positioned on the side of the user'shead to allow for the transmission of the coded sound signal from thespeech processor and power to the implanted stimulator unit.

[0011] With further improvements in technology becoming available, it isenvisaged that in the future it may be possible to provide a cochlearimplant that is capable of being totally implanted in an implantee andcan operate, at least for a portion of time, without the need for anyexternal devices. Such a device would have an implanted power source andmicrophone and would be able to perform speech processing functionswithout the need for an external device and associated link.

[0012] Together with improvements in available technology much researchhas been undertaken in the area of understanding the way sound isnaturally processed by the human auditory system. With such an increasedunderstanding of how the cochlea naturally processes sounds of varyingfrequency and magnitude, there is a need to provide an improved cochlearimplant system that delivers electrical stimulation to the auditorynerve in a way that takes into account the natural characteristics ofthe cochlea.

[0013] It is known in the art that the cochlea is tonotopically mapped.In other words, the cochlea can be partitioned into regions, with eachregion being responsive to signals in a particular frequency range. Thisproperty of the cochlea is exploited by providing the electrode assemblywith an array of electrodes, each electrode being arranged andconstructed to deliver a cochlea stimulating signal within a preselectedfrequency range to the appropriate cochlea region. The electricalcurrents and electric fields from each electrode stimulate the ciliadisposed on the modiola of the cochlea. Several electrodes may be activesimultaneously.

[0014] It has been found that in order for these electrodes to beeffective, the magnitude of the currents flowing from these electrodesand the intensity of the corresponding electric fields, are a functionof the distance between the electrodes and the modiola. If this distanceis relatively great, the threshold current magnitude must be larger thanif the distance is relatively small. Moreover, the current from eachelectrode may flow in all directions, and the electrical fieldscorresponding to adjacent electrodes may overlap, thereby causingcross-electrode interference. In order to reduce the thresholdstimulation amplitude and to eliminate cross-electrode interference, itis advisable to keep the distance between the electrode array and themodiola as small as possible. This is best accomplished by providing theelectrode array in the shape which generally follows the shape of themodiola. Also, this way the delivery of the electrical stimulation tothe auditory nerve is most effective as the electrode contacts are asclose to the auditory nerves that are particularly responsive toselected pitches of sound waves.

[0015] In order to achieve this electrode array position close to theinside wall of the cochlea, the electrode needs to be designed in such away that it assumes this position upon or immediately followinginsertion into the cochlea. This is a challenge as the array needs to beshaped such that it assumes a curved shape to conform with the shape ofthe modiola and must also be shaped such that the insertion processcauses minimal trauma to the sensitive structures of the cochlea. Inthis sense it has been found to be desirable for the electrode array begenerally straight during the insertion procedure.

[0016] Several procedures have been adopted to provide an electrodeassembly that is relatively straightforward to insert while adopting acurved configuration following insertion in the cochlea. In one case, aplatinum wire stylet is used to hold a pre-curved electrode array in agenerally straight configuration up until insertion. Followinginsertion, the platinum stylet is withdrawn allowing the array to returnto its pre-curved configuration.

[0017] The present invention is directed to an electrode assembly thatcan preferably be inserted more deeply into the cochlea whilst alsopreferably reducing the degree of trauma to the sensitive structureswithin the cochlea. A method of manufacturing such an electrode assemblyis also described.

[0018] Any discussion of documents, acts, materials, devices, articlesor the like which has been included in the present specification issolely for the purpose of providing a context for the present invention.It is not to be taken as an admission that any or all of these mattersform part of the prior art base or were common general knowledge in thefield relevant to the present invention as it existed in Australiabefore the priority date of each claim of this application.

SUMMARY OF THE INVENTION

[0019] Throughout this specification the word “comprise”, or variationssuch as “comprises” or “comprising”, will be understood to imply theinclusion of a stated element, integer or step, or group of elements,integers or steps, but not the exclusion of any other element, integeror step, or group of elements, integers or steps.

[0020] According to a first aspect, the present invention is animplantable electrode array that can adopt a first configurationselected to allow the array to be inserted into a cochlea of animplantee and at least a second configuration in which the array canapply tissue stimulation, the array comprising:

[0021] an elongate carrier having a proximal end, a distal end, and aninner surface conformable with the inner wall of the implantee'scochlea; and

[0022] a plurality of electrodes supported within the carrier atrespective spaced locations thereon in a region between the proximal endand the distal end, at least one of the electrodes having a surface thatis at least adjacent the inner surface of the carrier;

[0023] wherein the carrier is formed in said second configuration from afirst layer and at least a second layer of resiliently flexiblematerial.

[0024] In a first embodiment, each of the electrodes in the array have asurface that is at least adjacent the inner surface of the carrier. In afurther embodiment, the surfaces of the electrodes are aligned with theinner surface of the carrier. In another embodiment, the surfaces of theelectrodes stand proud of the inner surface of the carrier. It is alsoenvisaged that the electrode surface could also be recessed into theinner surface of the carrier.

[0025] In a first embodiment, the first layer can overlay each of theelectrodes except their said respective surfaces adjacent the innersurface of the carrier. The first layer preferably extends for at leasta portion of the length of the carrier. The first layer can extend fromthe proximal end to the distal end of the carrier. The second layer alsopreferably extends for at least a portion of the length of the carrier.The second layer can also extend from the proximal end to the distal endof the carrier.

[0026] In a further embodiment, the second layer can overlay at least aportion of an outer surface of the first layer. The second layer canoverlay a majority of the outer surface of the first layer, and stillmore preferably can overlay the entire outer surface of the first layer.

[0027] In one embodiment, the first layer and second layer can be formedfrom different materials. In another embodiment, the first and secondlayers can be formed from the same material. In one embodiment, thefirst and second layers can each be formed from a medical grade,biocompatible elastomeric material. In one embodiment, the elastomericmaterial can be a silicone rubber. In another embodiment, tile elongatemember can be formed from a polyurethane or similar material.

[0028] In a further embodiment, the thickness of the first layer betweenits inner surface and outer surface can be substantially constant for atleast a majority of its length from the proximal end to the distal end.In another embodiment, the thickness of the first layer can change, suchas decrease, from the proximal end to the distal end. In a furtherembodiment, the thickness of the second layer can be constant for atleast a majority of its length. In a still further embodiment, thethickness of the second layer can change, such as decrease, from theproximal end to the distal end.

[0029] In a still further embodiment, the thickness of the second layercan be substantially the same as the first layer. It can, however, beenvisaged that the thickness of the second layer may be greater than orless than the diameter of the first layer of the carrier.

[0030] In one embodiment, the second layer is bonded to the first layer.The bonding can be provided by an adhesive layer or can be achieved bybringing the layers together while in a state that results in bondingtogether of the respective layers.

[0031] In a preferred embodiment, the implantable electrode array is acochlear implant electrode array, with the carrier being adapted forinsertion into the cochlea of an implantee. Preferably, the carrier isadapted for insertion into the scala tympani of the cochlea of theimplantee.

[0032] In a preferred embodiment, the second configuration of thecarrier is preferably a curved configuration. Preferably, the curvedconfiguration is such that the carrier can fit inside the cochlea of theimplantee with said adjacent surfaces of the electrodes being orientedto face the modiolus of the cochlea.

[0033] The outer surface of the second layer of the carrier ispreferably smooth to prevent any damage to the cochlea as the carrier isinserted into the cochlea.

[0034] In a further embodiment, the carrier can have a lumen extendinglongitudinally from an opening at the proximal end into the carrier. Thelumen can extend to a position close to the distal end of the carrier.The lumen can be positioned in the first layer or the second layer. Inanother embodiment, the lumen can be positioned between the first andsecond layers. The lumen can be cylindrical or have any other suitablecross-sectional shape. The proximal opening of the lumen can be closableby a closure means adapted to seal the opening of the lumen.

[0035] The electrode array can be provided with a stiffening elementthat is sized to fit into the lumen and extend substantially through thecarrier. When the stiffening element is within the lumen, the carriercan be biased into a first, substantially straight, configuration inwhich the carrier is insertable into the cochlea of the implantee.

[0036] In a preferred embodiment, the lumen has a cross-sectionaldimension which decreases as the elongate carrier changes shape from thesubstantially straight first configuration to a curved configuration toallow, if desired, the stiffening element to be withdrawn.

[0037] The stiffening element can comprise a stylet formed from amalleable and biocompatible material. The stylet can be formed from asuitable metal, such as platinum, or a metallic alloy or relativelystiff plastics material.

[0038] In another embodiment, the stiffening element can be formed froma bioresorbable material which softens or dissolves on exposure to afluid. The stiffening element can soften or dissolve on exposure to asaline solution or a body fluid of the implantee, such as cochlearfluid.

[0039] In a further embodiment, the bioresorbable material of thestiffening element is selected from the group consisting of polyacrylicacid (PAA), polyvinyl alcohol (PVA), polylactic acid (PLA) andpolyglycolic acid (PGA). It is envisaged that other similar materialscould also be used.

[0040] In a still further embodiment, the stiffening element can beformed from a shape memory material. For example, the stiffening elementcan be formed from a nickel-titanium alloy or Nitinol™ and shaped totake a straight or substantially straight configuration at roomtemperature but bends into another shape on exposure to bodytemperature.

[0041] In a further embodiment, the stylet can include a tip, the tipbeing more flexible than the remainder of the stylet.

[0042] The carrier can also include a tip member, the tip member beingstraighter than the rest of the elongate carrier. The tip member is alsopreferably more flexible than the remainder of the stylet. In a furtherembodiment, the stylet can have a variable stiffness.

[0043] In a preferred embodiment, the electrode array can includeelectrically conducting wires connected to the electrodes and extendingto at least said proximal end. In one embodiment, one wire can beconnected to each of said electrodes. In another embodiment, at least towires can be connected to each of said electrodes.

[0044] Each electrode can comprise a contact member. The carrier canhave a longitudinal axis with each contact member arranged orthogonallyto the longitudinal axis. The contact members can be formed from abiocompatible material. The biocompatible material can be platinum. Thewires are preferably connected to the contact members by welding.

[0045] The carrier of the electrode array preferably naturally adopts aspiral configuration. In a preferred embodiment, the spiral carriersubtends an arc greater than 450°.

[0046] In yet a further embodiment, the lumen in the carrier can act asa substance delivery means for delivering a bio-active substance to theimplant site following implantation. In an alternative embodiment,another lumen can be formed in the carrier to act as the substancedelivery means.

[0047] The lumen can act as a reservoir for the bio-active substance. Inone embodiment, the bio-active substance in the reservoir can leach fromthe lumen into the surrounding material of the carrier and eventuallymigrate to an outer surface of the carrier, such as the inner surface ofthe first layer, that is preferably close to the desired site of actionfor the bio-active substance. In another embodiment, the carrier canhave one or more substance egress means whereby the bio-active substancecan move out of the lumen and through the carrier to a position that ispreferably close to the desired site of action for the bio-activesubstance.

[0048] Where the bio-active substance is carried in or comprises afluid, each substance egress means preferably comprises a fluid egressmeans.

[0049] Each fluid egress means preferably has a valve means that allowsfluid to exit the lumen but prevents, or at least substantiallyprevents, fluid flow from external the elongate member back into thelumen within the carrier.

[0050] In a further embodiment, the proximal opening of the lumen can bein fluid communication with an additional reservoir for the bio-activesubstance that is external to the carrier. A pumping means, such as anosmotic pump, can transfer the bio-active substance from the additionalreservoir into the lumen of the carrier for subsequent delivery to theappropriate site of action.

[0051] It is also envisaged that the bio-active substance can becaptured in the form of a solid pellet. An example of how this may occuris by impregnating the bio-active substance in a ceramic or a polymerpellet that has a predetermined rate of release of the bio-activesubstance. This solid pellet can then be stored in the lumen reservoiror in an external reservoir connectable to the lumen.

[0052] In another embodiment, a stiffening element made from abioresorbable material can also be impregnated with one or more of thebio-active substances allowing the stiffening element to perform a dualrole. The rate of delivery of the bio-active substance can be programmedby design of the element structure.

[0053] In one embodiment, the bioactive substance can comprise asteroid. In another embodiment, the bioactive substance can perform afunction of reducing the resting neuron potential of neurons within thecochlea. The use of such substances can result in less energy beingrequired to excite the neurons and cause stimulation.

[0054] In a still further embodiment, at least a portion of the outersurface of the carrier can have a coating of lubricious material. In afurther embodiment, a substantial portion of the outer surface can havea coating of the lubricious material. In a still further embodiment, theentire outer surface of the carrier can have a coating of the lubriciousmaterial.

[0055] The lubricious material preferably becomes lubricious on beingbrought into contact with a fluid, such as a saline solution. Stillfurther, the coating preferably becomes lubricious on being brought intocontact with a body fluid, such as cochlear fluid.

[0056] In one embodiment, the lubricious material is selected from thegroup consisting of polyacrylic acid (PAA), polyvinyl alcohol (PVA),polylactic acid (PLA) and polygiycolic acid (PGA). It is envisaged thatother similar materials could also be used. It is envisaged that thelubricious material can also be impregnated with the bio-activesubstance allowing the coating to perform a dual role. The rate ofdelivery of the bio-active substance can be programmed by design of thecoating structure.

[0057] In a still further embodiment, the carrier can be enveloped by astiffening sheath which is made of a material that is relatively stifferthan the resiliently flexible material of the carrier. The stiffeningsheath can be adapted to bias the carrier into a substantially straightconfiguration. In one embodiment, the stiffening sheath can be overlaidby the coating of lubricious material.

[0058] Where both the stiffening element and stiffening sheath arepresent in the device, the element and sheath can be adapted incombination to bias the carrier into the substantially straightconfiguration. In this embodiment, if either the stiffening element orthe stiffening sheath is removed or deactivated, the carrier can adoptat least one intermediate configuration. In this embodiment, thestiffening sheath can be formed of the same material or a differentmaterial to that of the stiffening element. In either case, thestiffening sheath can be relatively more stiffer or relatively lessstiffer than the stiffening element.

[0059] The stiffening sheath, if present, can be formed of abioresorbable material which dissolves or softens on exposure to afluid. The stiffening sheath can dissolve or soften on exposure to asaline solution or a body fluid of the implantee, such as cochlear fluidand in doing so also release one or more bio-active substancesimpregnated therein.

[0060] In a further embodiment, the bioresorbable material of thestiffening sheath is selected from the group consisting of polyacrylicacid (PAA), polyvinyl alcohol (PVA), polylactic acid (PLA) andpolyglycolic acid (PGA). It is also envisaged that other suitablematerials could also be used. It is envisaged that the bioresorbableelement of the stiffening sheath can also be impregnated with one ormore bio-active substances allowing the stiffening sheath to perform adual role. The rate of delivery of the bio-active substance can beprogrammed by design of the sheath structure.

[0061] The carrier can include an additional layer surrounding thestiffening sheath. The additional layer can have a first rate of fluidingress therethrough and have at least one fluid ingress means formedtherein, the rate of fluid ingress through the fluid ingress means beinggreater than the first rate of fluid ingress through the additionallayer. In this embodiment, the coating of lubricious material can becoated on the outside of the additional layer.

[0062] The fluid ingress means can comprise one or more openings in theadditional layer. The openings can be closable. The openings cancomprise slits in the additional layer. The slits can be formed to allowsubstantially the same or the same rate of ingress of fluid through theadditional layer. In another embodiment at least one slit can allow adifferent rate of progress of fluid through the additional layercompared to the other slits.

[0063] The stiffening sheath, if present, can be formed from a shapememory or heat sensitive material. For example, the stiffening sheathcan be formed from a nickel-titanium alloy or Nitinol™ and shaped totake and maintain the straight or substantially straight configurationof the carrier at room temperature but bends it into another shape onceit is exposed to body temperature.

[0064] In one embodiment, while both the stiffening element and thestiffening sheath are in position within the carrier, it will retain thefirst substantially straight configuration. If the stiffening sheath isremoved or softened, whether it is by dissolution or otherwise, theremaining stiffening element can have insufficient strength to retainthe carrier in its first configuration. It is preferred that thecarrier, on removal or softening of the stiffening sheath, will adopt anintermediate configuration in which the carrier has at least somecurvature.

[0065] The present invention provides a surgeon with a cochlear implantelectrode array that can potentially be inserted to a greater degreethan hitherto known electrode arrays whilst maintaining close proximitybetween the surfaces of the electrodes and the modiolus.

[0066] According to another aspect, the present invention is animplantable electrode array for insertion into the cochlea of animplantee, said array comprising:

[0067] a first layer made of a resiliently flexible material andsupporting a plurality of electrodes within said first layer with atleast one of said electrodes having a surface that is at least adjacentthe inner surface of the first layer, said first layer being of a curvedconfiguration;

[0068] at least a second layer made of resiliently flexible material andoverlaying an outer surface of the first layer, said at least secondlayer also being of a curved configuration;

[0069] wherein the plurality of layers together form a pre-curvedelectrode carrier capable of applying tissue stimulation.

[0070] In this aspect, the degree of curvature of the first layer isgreater than that of the at least second layer.

[0071] The degree of curvature of the electrode carrier can becontrolled by altering one or both of the degrees of curvature of thefirst and at least second layers.

[0072] Each of the electrodes in the first layer have a surface that isat least adjacent the inner surface of the carrier.

[0073] In another aspect, the present invention is an implantableelectrode array for insertion into the cochlea of an implantee, saidarray comprising:

[0074] a first layer made of a resiliently flexible material and havinga curved configuration and a first degree of curvature;

[0075] at least a second layer made of a resiliently flexible materialand having a curved configuration and a second degree of curvature;

[0076] wherein the layers in combination form an electrode array havinga degree of curvature dependent on the respective degrees of curvatureof the first layer and the at least second layer.

[0077] In this aspect, the first layer has a greater degree of curvaturethan the at least second layer.

[0078] According to a further aspect, the present invention is a methodof manufacturing an implantable electrode array, the method comprisingthe steps of:

[0079] (i) moulding a first layer of an elongated carrier from aresiliently flexible material about a longitudinal array of electrodessuch that at least one of the electrodes has a surface that is at leastadjacent an inner surface of the carrier; and

[0080] (ii) moulding a second layer of the carrier from a resilientlyflexible material over at least a portion of the surface of the firstlayer other than its inner surface.

[0081] In a preferred embodiment, the electrodes can comprise aplurality of rings. The formed carrier can have a longitudinal axis witheach electrode arranged orthogonally to the longitudinal axis. Theelectrodes can be formed from a biocompatible material, such asplatinum. The electrode array is preferably formed by positioning aseries of platinum rings on or about a longitudinal support that ispreferably removable once the carrier has been moulded about theelectrodes. The support can comprise a wire that is coated with alow-friction material, such as polytetrafluroethylene (PTFE).

[0082] Once positioned about the PTFE-coated wire, a series ofelectrically conducting wires can be welded to each of the electrodes.Each electrode preferably has at least one, and more preferably two,electrically conducting wires welded thereto.

[0083] Once the electrodes are positioned about the PTEE-coated wire,the array is placed in a first mould to allow formation of the firstlayer. In a preferred embodiment, the carrier is adapted for insertioninto the cochlea. As such, it is preferred that the array is placed in aspiral-shaped mould. The spiral-shaped mould preferably subtends an arcof greater than 720°. The mould is preferably specifically adapted toform a first layer of the carrier in which the spiral shape of the firstlayer subtends an arc greater than the carrier ultimately formed by themethod when the second layer is moulded thereto.

[0084] The first layer is preferably formed from an elastomeric siliconematerial and remains in the first mould until cured.

[0085] Once cured, the formed first layer of the carrier is removed fromthe first mould. The first layer can then be placed in a second mouldhaving a set of dimensions generally greater than the first mould. Inthe case of a cochlear implant array, the second mould again preferablycomprises a spiral-shaped mould. The second mould typically subtends anarc less than that of the first mould. In one embodiment, the secondmould subtends an arc of about 180° less than the arc subtended by thefirst mould.

[0086] On placement of the first layer in the second mould, the innersurface of the first layer is preferably adapted to abut with the innersurface of the second mould. Given that the first layer has been formedin a first mould having smaller dimensions and a relatively tighterdegree of curvature, the first layer will preferentially abut the innersurface of the second mould. This serves to ensure that the electrodesthat are positioned adjacent the inner surface are not coated with alayer of elastomeric material when the second layer is moulded to thefirst layer in the second mould.

[0087] The second layer is preferably formed from a elastomeric siliconematerial, with the carrier remaining in the second mould until thesecond layer is cured. The second layer can be formed from the samematerial as the first layer or a different material.

[0088] Once the second layer is cured, the carrier can be removed fromthe second mould and straightened. The carrier may be straightened byand held straight in a straightening jig.

[0089] Once at least substantially straightened, the PTFE-coated wirecan be gently removed from within the carrier. The removal of thePTFE-coated wire results in the formation of a lumen within the firstlayer of the carrier.

[0090] If desired, while still being held at least substantiallystraight, a straightening element, such as a metallic stylet ornon-metallic stylet-like member can be inserted into the lumen to holdthe carrier in the straightened configuration until such time, as thecarrier is to be inserted into a cochlea.

[0091] In a still further aspect, the present invention is animplantable electrode array when formed using the method of the furtheraspect defined above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0092] By way of example only, a preferred embodiment of the inventionis now described with reference to the accompanying drawings, in which:

[0093]FIG. 1 is a simplified pictorial representation of a prior artcochlear implant system; and

[0094]FIG. 2 is a plan view of PTFE-coated wire having a plurality ofplatinum ring electrodes mounted thereon;

[0095]FIG. 3 is a sectional view of a first layer of an elongatedcarrier according to the present invention;

[0096]FIG. 4 is a plan view depicting the first layer of FIG. 3positioned in a second mould ready for moulding of the second layer ofthe carrier; and

[0097]FIG. 5 is a cross-sectional view of an elongate carrier for acochlear implant electrode array according to the present inventionhaving both a first and second layer.

PREFERRED MODE OF CARRYING OUT THE INVENTION

[0098] Before describing the features of the present invention, it isappropriate to briefly describe the construction of one type of knowncochlear implant system with reference to FIG. 1.

[0099] Known cochlear implants typically consist of two main components,an external component including a speech processor 29, and an internalcomponent including an implanted receiver and stimulator unit 22. Theexternal component includes a microphone 27. The speech processor 29 is,in this illustration, constructed and arranged so that it can fit behindthe outer ear 11. Alternative versions may be worn on the body. Attachedto the speech processor 29 is a transmitter coil 24 which transmitselectrical signals to the implanted unit 22 via a radio frequency (RF)link.

[0100] The implanted component includes a receiver coil 23 for receivingpower and data from the transmitter coil 24. A cable 21 extends from theimplanted receiver and stimulator unit 22 to the cochlea 12 andterminates in an electrode array 20. The signals thus received areapplied by the array 20 to the basilar membrane 8 and the nerve cellswithin the cochlea 12 thereby stimulating the auditory nerve 9. Theoperation of such a device is described, for example, in U.S. Pat. No.4,532,930.

[0101] As depicted diagrammatically in FIG. 1, the cochlear implantelectrode array 20 has traditionally been inserted into the initialportion of the scala tympani of the cochlea 12, and typically up toabout a full turn within the cochlea. The electrode array according tothe present invention is adapted to be inserted more deeply into thecochlea 12 than has historically been the case. For the purpose of theremainder of the specification, one embodiment of a cochlear implantelectrode array is depicted generally as 30 in FIG. 5.

[0102] The array 30 comprises an elongate electrode carrier member 31.The depicted elongate member 31 is preformed from a first layer 32 and asecond layer 33 of resiliently flexible silicone with memory and isformed in a curved configuration suitable for placement in the scalatympani of a human cochlea 12. In the depicted embodiments, each layer32,33 is formed from the same elastomeric silicone material. It will beunderstood by a person skilled in the art that the layers 32,33 could beformed from different materials to one another should a particularcharacteristic of the material be desired.

[0103] The elongate member 31 has a first distal end 34 that is firstlyinserted into the cochlea 12 upon insertion of the array 30. Theelongate member also has an inner surface 35 adapted to be positioned atleast close to the surface of the modiolus of the cochlea 12 followinginsertion of the array 30. Disposed within the first layer are aplurality of electrodes 36. It will be appreciated that the electrodes36 depicted in FIG. 5 are not necessarily drawn to scale.

[0104] Further, more or less electrodes than that depicted in FIG. 5could be utilised in the elongate member 31. Each electrode 36 comprisesa platinum contact surface having an outer surface at least adjacent,and preferably substantially aligned with, the inner surface 35 of thefirst layer 32 of the elongate member 31. While not depicted, it will beunderstood that at least one electrically conducting wire would extendfrom each of the electrodes 36 through the elongate member 31 to atleast the depicted end 37 of the member 31. The wires would normallyextend back to an implanted stimulator/receiver unit, such as unit 22depicted in FIG. 1.

[0105] Disposed longitudinally through the first layer 32 is a lumen 38.It may also be possible to have more than one lumen extendinglongitudinally through the array 30. The lumen 38 can have a number ofuses. While depicted in the first layer 32, the lumen could extendlongitudinally through the second layer 33 or even further, a lumencould be provided in both layers, 32 and 33. It could also be positionedat the longitudinal join between the first and second layers 32,33.

[0106] The lumen 38 can have disposed therein, prior to insertion of theassembly 30 into the cochlea 12, a substantially straight platinumstylet. The stylet can have a stiffness that is sufficient to retain thesilicone elongate member 31 in a straight configuration. It will beappreciated that the stylet could be constructed so as to have astiffness that was insufficient alone to retain the elongate member 31in a straight configuration.

[0107] Instead of a platinum stylet, a bioresorbable stylet-like memberformed from a bioresorbable polyacrylic acid (PAA) which is adapted todissolve or soften on exposure to cochlear fluids, could be utilisedwith appropriate modification to the elongate carrier member 31. Astiffening polymer stylet could also be utilised. Both such embodimentsof a polymeric stylet could also be impregnated with a bio-activesubstance.

[0108] A bioresorbable stylet would preferably soften quickly, but notdissolve quickly, with its very slow dissolution rate allowing anyimpregnated bioactive substance to effectively elute to the body.

[0109] Whilst a substantially cylindrical lumen is depicted, the lumen38 could be any shape necessary to perform the function.

[0110] If used, a stylet-like member from a bioresorbable material canhave a stiffness that is either sufficient or insufficient to retain thesilcone elongate member 31 in a straight configuration. It will beappreciated that a bioresorbable stylet-like member could be formed fromother suitable bioresorbable materials. A stylet-like member made from ashape memory material could also be utilised instead of a platinumstylet.

[0111] While the depicted elongate member 31 is manufactured in a curvedconfiguration, the array 30 is typically delivered to a surgeon in asterile package with a stylet or stylet-like member in place.

[0112] On removal from the package and insertion into the scala tympaniof the cochlea 12, the platinum stylet can be withdrawn to allow theelongate member 31 to commence to adopt its naturally curvedconfiguration, with the electrodes 36 facing the modiolus within thecochlea 12 so that they are positioned as close as possible to thespiral ganglia thereof.

[0113] The provision of a cochlear implant electrode array 30 having afirst and second layer 32,33 allows the elongate member 31 to beinserted, in a typical case, more deeply into the scala tympani of thecochlea 12 than would be the case for hitherto traditionally usedarrays, such as array 20 depicted in FIG. 1.

[0114] To form the electrode array 30 depicted in FIG. 5, a plurality ofplatinum rings, which become the electrodes 36, are mounted on aPTEE-coated wire 39. While not depicted, each ring 36 has preferably atleast two conductive wires welded thereto to allow electrical connectionfrom the implanted stimulator/receiver unit 22 to the rings 36.

[0115] Once formed, the electrode assembly depicted in FIG. 2 is placedin a first spiral-shaped mould, with the outer surfaces of the rings 36abutting the inner surface thereof. The spiral of the first mouldpreferably subtends an arc of greater than 720°. Once correctlypositioned in the first mould, a silicone is poured/injected into thefirst mould around the wire 39 and allowed to cure. Once cured, theformed elastomeric first layer 32 can be removed from the first mould.As depicted in FIG. 3, the PTFE-coated wire 39 is preferably left inplace following removal from the first mould.

[0116] Once removed from the first mould, the first layer 32 can bepositioned in a second mould, such as the spiral mould 50 depicted inFIG. 4. The mould 50 has a spiral-shaped channel 51 formed therein. Thechannel 51 subtends an arc that is about 180° less than the arcsubtended by the equivalent channel in the first mould (not depicted).

[0117] As the relaxed condition of the first layer 32 has a tighterdegree of curvature than the curvature of the channel 51, the innersurface 35 of the first layer 32 abuts with the inner surface 52 of thechannel 51 on being placed therein.

[0118] Once positioned in the second mould 50, a further quantity ofsilicone can be poured/injected into the mould and allowed to cure. Thefurther quantity of silicone forms the second layer 33 of the elongatemember 31 depicted in FIG. 5.

[0119] Once the second layer is cured, the elongate member 31 can beremoved from the second mould 50. If desired, the elongate member 31 canthen be placed in a straightening jig before the PTFE-coated wire 39 isremoved from the member 31. The removal of the wire 39 leaves alongitudinal lumen 38 in the first layer 32 as already described herein.

[0120] The use of a two-step process as defined herein results in theformation of an elongate member having a greater degree of curvaturethan hitherto known in traditional cochlear implant electrode arrays.Further to this, the use of a two-step process of the present inventionallows for the width and thickness of the electrode array to be moreeasily modified to provide for a thinner array if desired.

[0121] While the preferred embodiment of the invention has beendescribed in conjunction with a cochlear implant, it is to be understoodthat the present invention has wider application to other implantableelectrodes, such as electrodes used with pacemakers and the like.

[0122] It will be appreciated by persons skilled in the art thatnumerous variations and/or modifications may be made to the invention asshown in the specific embodiments without departing from the spirit orscope of the invention as broadly described. The present embodimentsare, therefore, to be considered in all respects as illustrative and notrestrictive.

1. An implantable electrode array that can adopt a first configurationselected to allow the array to be inserted into a cochlea of animplantee and at least a second configuration in which the array canapply tissue stimulation, the array comprising: an elongate carrierhaving a proximal end, a distal end, and an inner surface conformablewith the inner wall of the implantee's cochlea; and a plurality ofelectrodes supported within the carrier at respective spaced locationsthereon in a region between the proximal end and the distal end, atleast one of the electrodes having a surface that is at least adjacentthe inner surface of the carrier; wherein the carrier is formed in saidsecond configuration from a first layer and at least a second layer ofresiliently flexible material.
 2. An implantable electrode array ofclaim 1 wherein each of the electrodes in the array have a surface thatis at least adjacent the inner surface of the carrier.
 3. An implantableelectrode array of claim 2 wherein the surfaces of the electrodes arealigned with the inner surface of the carrier.
 4. An implantableelectrode array of claim 1 wherein the first layer overlies each of theelectrodes except their said respective surfaces at least adjacent theinner surface of the carrier.
 5. An implantable electrode array of claim1 wherein the first layer extends from the proximal end to the distalend of the carrier.
 6. An implantable electrode array of claim 5 whereinthe second layer extends from the proximal end to the distal end of thecarrier and overlies the entire outer surface of the first layer.
 7. Animplantable electrode array of claim 1 wherein the first layer andsecond layer are formed from different materials.
 8. An implantableelectrode array of claim 1 wherein the first and second layers areformed from the same material.
 9. An implantable electrode array ofclaim 8 wherein the first and second layers are each formed from abiocompatible silicone rubber.
 10. An implantable electrode array ofclaim 1 wherein the thickness of the first layer between its innersurface and outer surface is substantially constant for at least amajority of its length from the proximal end to the distal end.
 11. Animplantable electrode array of claim 1 wherein the thickness of thefirst layer decreases from the proximal end to the distal end.
 12. Animplantable electrode array of claim 11 wherein the thickness of thesecond layer decreases from the proximal end to the distal end.
 13. Animplantable electrode array of claim 1 wherein the second configurationcomprises a spiral configuration.
 14. An implantable electrode array ofclaim 1 wherein the carrier has a lumen extending longitudinally from anopening at the proximal end into the carrier and adapted to receive astiffening element that is sized to fit into the lumen and extendsubstantially through the carrier to bias the carrier into the firstconfiguration in which the carrier is insertable into the cochlea of theimplantee.
 15. An implantable electrode array of claim 14 wherein thefirst configuration is straight or substantially straight.
 16. Animplantable electrode array of claim 1 wherein at least a portion of theouter surface of the carrier has a coating of a material that becomeslubricious on being brought into contact with a fluid, said materialbeing selected from the group consisting of polyacrylic acid (PAA),polyvinyl alcohol (PVA), polylactic acid (PLA) and polyglycolic acid(PGA).
 17. A method of manufacturing an implantable electrode array, themethod comprising the steps of: (i) moulding a first layer of anelongated carrier from a resiliently flexible material about alongitudinal array of electrodes such that at least one of theelectrodes has a surface that is at least adjacent an inner surface ofthe carrier; and (ii) moulding a second layer of the carrier from aresiliently flexible material over at least a portion of the surface ofthe first layer other than its inner surface.
 18. A method ofmanufacturing an implantable electrode array of claim 17 wherein thearray of electrodes is formed by positioning a series of platinum ringson or about a removable longitudinal support.
 19. A method ofmanufacturing an implantable electrode array of claim 18 wherein thesupport comprises a wire coated with a relatively low-friction material.20. A method of manufacturing an implantable electrode array of claim 19wherein once positioned about the wire, a series of electricallyconducting wires are welded to each of the electrodes.
 21. A method ofmanufacturing an implantable electrode array of claim 20 wherein thefirst layer is moulded in a first spiral-shaped mould.
 22. A method ofmanufacturing an implantable electrode array of claim 21 wherein thespiral-shaped mould subtends an arc of greater than about 720°.
 23. Amethod of manufacturing an implantable electrode array of claim 22wherein the first layer, once cured, is removed from the first mould andplaced in a second mould having a set of dimensions greater than thefirst mould.
 24. A method of manufacturing an implantable electrodearray of claim 23 wherein the second mould comprises a spiral-shapedmould having at least an inner surface and which subtends an arc lessthan that of the first mould.
 25. A method of manufacturing animplantable electrode array of claim 24 wherein the second mouldsubtends an arc of about 180° less than the arc subtended by the firstmould.
 26. A method of manufacturing an implantable electrode array ofclaim 25 wherein on placement of the first layer in the second mould,the inner surface of the first layer abuts with the inner surface of thesecond mould.
 27. A method of manufacturing an implantable electrodearray of claim 26 wherein once the second layer is cured, the carrier isremoved from the second mould and straightened.
 28. A method ofmanufacturing an implantable electrode array of claim 27 wherein oncethe carrier is straightened, the wire is removed from within the carrierso leaving a lumen within the first layer of the carrier.
 29. A methodof manufacturing an implantable electrode array of claim 28 whereinwhile the carrier is held at least substantially straight, astraightening element is inserted into the lumen to hold the carrier inthe straightened configuration until such time as the carrier is to beinserted into a cochlea.
 30. An implantable electrode array when formedusing the method of any one of claims 17 to
 29. 31. An implantableelectrode array for insertion into the cochlea of an implantee, saidarray comprising: a first layer made of a resiliently flexible materialand supporting a plurality of electrodes within said first layer with atleast one of said electrodes having a surface that is at least adjacentthe inner surface of the first layer, said first layer being of a curvedconfiguration; at least a second layer made of resiliently flexiblematerial and overlaying an outer surface of the first layer, said atleast second layer also being of a curved configuration; wherein theplurality of layers together form a pre-curved electrode carrier capableof applying tissue stimulation.
 32. An implantable electrode array ofclaim 31 wherein the degree of curvature of the first layer is greaterthan that of the at least second layer.
 33. An implantable electrodearray of claim 31 wherein the degree of curvature of the electrodecarrier can be controlled by altering one or both of the degrees ofcurvature of the first and at least second layers.
 34. An implantableelectrode array of claim 31 wherein each of the electrodes in the firstlayer have a surface that is at least adjacent the inner surface of thecarrier.
 35. An implantable electrode array for insertion into thecochlea of an implantee, said array comprising: a first layer made of aresiliently flexible material and having a curved configuration and afirst degree of curvature; at least a second layer made of a resilientlyflexible material and having a curved configuration and a second degreeof curvature; wherein the layers in combination form an electrode arrayhaving a degree of curvature dependent on the respective degrees ofcurvature of the first layer and the at least second layer.
 36. Animplantable electrode array of claim 35 wherein the first layer has agreater degree of curvature than the at least second layer.